The use of Hall-effect sensors or sensors with magneto-resistance in devices for determination of angular position is well known in the prior art, in particular for the purpose of controlling certain rotary electrical machines which are used in the automobile industry.
An example of these devices is given in international patent application WO2006/010864 by the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR.
The signals which are provided by the sensors, generally comprising a high level of harmonics, must sometimes be processed in order to obtain sinusoidal signals which permit better control of a multiphase electrical machine.
According to the teaching of the aforementioned application, certain particular linear combinations of unprocessed signals obtained from the sensors are free from harmonics, and close to the ideal sine wave form.
In U.S. Pat. No. 6,720,763, which also describes a resolver, a magnetic target, consisting of a multi-polar magnetic ring or disc, appears to create in the vicinity of the sensors a magnetic field which can produce as output sinusoidal signals without additional processing.
However, no precise information concerning the degree of purity of the sinusoidal signals obtained is disclosed.
In addition, it has been found experimentally by the applicant that this degree of purity, or the levels of harmonics of these signals were sensitive to the dispersions of assembly and mechanical tolerances of the different elements of the device, to the dispersions of the characteristics of the magnetic material of the target, and to the functioning temperature.
The aforementioned American patent also contains nothing about these points, which are crucial for the purpose of an industrial application.
A device is also known for angular determination, also known by the name of “resolver”, which is placed at the end of the rotor shaft of an alternator starter, and provides signals which are representative of the angular position of this rotor.